1. Field of the Invention
This invention relates to a gearbox comprising at least two parallel shafts carrying gear wheels permanently meshing with one another in pairs, one gear wheel of each pair being connectable to its associated shaft for torque transmission by a friction clutch which is engagable by an actuating means which operates axially on the clutch.
2. Description of Prior Art
Conventional automatic gearboxes comprising planetary gears, preferably with four speed ratios and with highest gears which are partly or completely direct driven (i.e. with the torque convertor wholly or partly switched off), meet the highest standards of economy and driving comfort. However, such gearboxes are technically complicated and expensive to manufacture.
Double-clutch gearboxes which, in principle, are designed like conventional manual gearboxes are able to shift gear ratio without interruption of power transmission. Shifting is effected by a double clutch arrangement and a shaft assembly comprising a hollow shaft and an inner shaft, which makes such gearboxes technically complex.
Conventional manual gearboxes can be automated, with clutch operation automatically controlled and operated in coordination with gear shifting. However, the coordination of clutch operation and gear shifting is difficult to control, and a disadvantage of such a gearbox is that power transmission must be interrupted for gear shifting.
GB-1582237 discloses an automatic gearbox wherein gear shift sleeves are replaced by hydraulically operated friction clutches, the hydraulic medium being supplied through bores extending axially in the gear shafts. However, the control of such supply of hydraulic medium is too complex for cost-effective production and trouble free operation.